The purpose of radio network dimensioning is to estimate the required number of radio base stations needed to support a specified traffic load in an area. The outcome of the dimensioning procedure is used in radio network design processes to get an early indication of network size and cost. The dimensioning phase is later followed by a planning phase during which more specific information is collected, enabling a more detailed analysis. Similar procedures may be used, for example, to determine the performance of a network having a given distribution of base stations.
The dimensioning process generally starts with an assumed network model. FIG. 1 shows such an assumed model. A number of hexagonal adjacent cells 1 each comprising a base station 3 are assumed. Further, within the area covered by the cells 1 a number of mobile terminals 5 are assumed. The assumed distribution of the mobile terminals may be arbitrary. Typically, a uniform distribution is selected. Thus, some terminals will be located close to a base station, others farther away. Some terminals will be located on the border between two cells.
The model typically comprises at least 30 cells and several thousand terminals. To obtain complete data for the network the path gain between each mobile terminal and each base station is determined. These path gain values are typically stored in a path gain matrix having one column for each cell and one row for each terminal. In the prior art three main methods for network dimensioning are known. The most accurate method involves simulating the behaviour in the network. This involves calculating the path gain matrix a large number of times. Typically, the simulations should cover a time span of several thousand seconds and the time between the calculations should not exceed 1 ms. Thus, in this method the path gain matrix must be calculated several million times. This provides detailed information but is very time consuming. With current computing resources one such simulation takes several hours. Therefore, this method is not practical for network dimensioning involving trial and error.
Simpler WCDMA dimensioning methods are known, which use calculations that utilize expressions aimed at determining power levels, e.g. the average power, for both capacity and coverage estimates corresponding to a fixed number of users in each cell. These average values are assumed to be constant throughout the calculations. Margins are added to compensate for traffic variations and randomness of the radio environment, e.g. shadow fading. In these methods, the values of the path gain matrix are condensed to a number of parameters that are used as input values for the calculation. Therefore, this method is faster than the simulation methods outlined above, but are less accurate. If the model is changed, the parameters should be calculated again, which is cumbersome. Therefore, the method is also not very flexible.
A more refined approach is the snapshot based simulation technique, which mainly targets network planning. In the snapshot approach, a number of independent samples of the network state are generated using assumed steady-state distributions for traffic and radio links. Appropriate performance statistics is collected in order to draw conclusions about coverage and capacity given the current network layout. The static snapshot simulations are sometimes complemented by short dynamic simulations in order to better take certain dynamic mechanisms into account. Full dynamic simulations are usually considered too cumbersome for dimensioning and planning since the search for suitable cell sizes might require a large number of time consuming simulations with different network configurations.